The present invention is in the field of sealed valves, and more particularly relates to a bellows-type valve that introduces very little contamination to the gas passing through it and that has an extremely low leak rate. Such valves find application in the semiconductor industry.
Two main types of valves that have been used in such applications are the diaphragm valve and the bellows valve. The diaphragm valve requires the use of nonlinear gas flows which can cause turbulance that might provoke the production of small particles and that might cause undesired pressure drops across the valve. The present invention is of the second type, in which the seat seal is attached to the end of a bellows that accommodates movement of the seat seal between the open and closed positions.
Traditional concerns regarding the use of bellows valves include the large area of the convoluted surface of the bellows and the large dead space of the chamber in which the bellows is housed.
Another traditional concern is that because the bellows is housed in a cylindrical chamber that extends away from the main flow path of the gas through the valve, the flow of gases cannot be relied upon to flush away contaminating particles from within the dead space immediately surrounding the bellows.
In spite of these disadvantages of bellows valves, such valves have redeeming features including a "straight through" gas flow path, a minimum of turbulance and a high flow coefficient.
As will be seen below, the present invention is directed at reducing the aforementioned disadvantages of the prior art bellows valves while retaining their advantages.